Grip head for an earth boring unit

ABSTRACT

The invention relates to a grip head for an earth boring unit, comprising a hollow shaft ( 3 ), wherein a sleeve ( 1 ) is arranged coaxially on the hollow shaft ( 3 ) to slide relative thereto, said sleeve having at least one end region ( 1   b ) widening particularly at the bottom thereof particularly in the form of a cone and at least two clamp jaws ( 2 ) which can be displaced radially relative to the hollow shaft ( 3 ) are arranged in the hollow shaft ( 3 ) and/or on the sleeve ( 1 ), comprising stop faces ( 2   b ) cooperating with the widening end region ( 1   b ), such that on movement of the end region ( 1   b ) over the clamp jaws ( 2 ) said jaws may be pressed inwards and a first tensioning mechanism and form a first tensioning device for an upper end of a casing ( 9 ) which may be introduced from below into the sleeve, in particular such that a cooperation between clamp jaws ( 2 ) and casing ( 9 ) permits transmission of a torque between ween the hollow shaft ( 3 ) and casing ( 9 ) and a second tensioning mechanism is provided in the hollow shaft ( 3 ), by means of which the introduced/introducible casing ( 9 ) may be fixed at the upper rend region thereof in the axial direction, in particular fixing a casing ( 9 ) in the axial direction against gravity relative to the grip head, wherein a flush tube ( 14 ) of supplying a flushing fluid is arranged coaxially in the hollow shaft ( 3 ) and fixed in rotation relative thereto the lower region of which is enclosed by an annular balloon ( 11 ) which may be pumped up with a fluid, in particular a liquid.

The invention relates to a grip head for earth-drilling system, comprising

a tube,

a sleeve provided coaxially on the tube so as to move relative thereto and having at least one lower end, in particular one widening downward, in particular widening in a frustoconical shape,

at least two jaws supported in the tube and/or on the sleeve so as to move radially relative to the tube, the jaws at their radially outer ends having abutment faces that interact with the widening lower end such that by sliding the lower end over the jaws they are pressed radially inward and form first grab means for an upper end of a casing that is insertable/inserted into the sleeve, in particular in such a way that due to the interaction between the jaws and the casing torque can be transmitted between the tube and the casing, and

second grab means provided in the tube for securing an inserted/insertable casing axially at its upper end, in particular so as to hold the casing stationary axially against gravity relative to the grip head.

A grip head of this type for use in well boreholes has already been disclosed by the instant applicant in German patent application DE 10 2008 012 729.9. The grip head described there, for which the interaction with a drill pipe was described, is in principle also capable of accommodating a casing, such as that described above, in place of a drill pipe.

Provision can be made in a first possible embodiment whereby the second grab means, just like the first grab means, is able to be actuated by moving the sleeve that is movable on the tube. This has the advantage for example that only one drive must be provided to move the sleeve.

In an alternative design, provision can also be made whereby the sleeve for actuating the first grab means is movable relative to the tube by a first drive, in particular a hydraulic drive, and the second grab means is actuatable by a second drive independent of the first drive, in particular where both drives are attached at one side to a common support element. As a result, both grab means can be operated independently of each other, for example either sequentially, but also simultaneously, for example, by synchronization in a master control unit that controls the drives. In both embodiments here, the drives can comprise, for example at least one, preferably, multiple cylinder-piston units distributed uniformly within the tube.

In the prior art, so-called casings have been used in connection with implementing well boreholes for the purpose of stabilizing the walls of the well borehole after drilling and after the drill pipe has been lifted out. To this end, provision is accordingly made whereby the casing is inserted into the bore created. The casing itself is hollow so that the inner free diameter of the bore is maintained; however, a long-term stabilization of the borehole is effectuated by the casing wall.

A problem is known in the prior art whereby well boreholes do not always follow a straight path, with the result that it is sometimes difficult to insert a casing into the borehole created in the ground after the dill pipe has been lifted out.

The object of the invention is thus to provide a grip head of the type described above that offers the ability to insert a casing into existing well boreholes in the ground at a later point in time, and in so doing to enable the casing not only to be inserted but also, in particular to be screwed into the borehole. In order here to achieve a facilitated insertion of the casing into the borehole, an additional goal is to use drilling mud, in particular water as a fluid, such that a concentration of the circulating force of the drilling mud within the borehole can be achieved.

This object is attained according to the invention by an approach wherein a circulation pipe for the delivery of a drilling mud extends coaxially in the tube and is rotationally fixed thereto, the lower end of the pipe being surrounded by an annular bladder inflatable in particular by a fluid.

The essential core idea in the construction of the grip head according to the invention is that a casing inserted in the grip head can be clamped securely first of all by the two grab means described above, and in particular by the movable jaws whose radial displacement clamps a casing inserted into the grip head securely in place so as to cause the casing in the ground to also rotate by rotation of the grip head. The above-referenced second grab means ensures here that an upper end, in particular of the casing, is held surely in place in the grip head, in particular against the force of gravity, so as to prevent the casing from sliding out of the grip head axially of the casing.

As was already described in the above-referenced document DE 10 2008 012 729.9, this makes it possible to rotationally insert a casing into the ground with the grip head in a manner analogous to the drill pipe described in the above-referenced document, where now in this embodiment according to the invention the ability is provided by the coaxial arrangement of the circulation pipe within an inserted or insertable casing to pump in drilling mud through the circulation pipe into the casing, such that the fluid moves through the casing down to its lower end, and in a region between the outer wall of the casing and the inner wall of the borehole contributes to loosening the borehole wall, to a kind of lubricating effect, and thus to an easier insertion of the casing into the borehole.

In order to achieve a good effective engagement between the jaws and a casing, the jaws of the first grab means can have, for example a surface formation on the face engaging the casing. For example, the surface can have a structuring, and/or a preferably a coating, that functions like a friction lining. This type of coating can for example have particles, for example sand, diamonds, etc., that enhance the effective engagement. As a result, the force can be applied over a large surface area to the casing, thereby avoiding any local damage.

According to the invention, a seal can be achieved here between the circulation pipe and the casing by the inflatable bladder that extends annularly around the circulation pipe in a region between circulation pipe and an inner wall of the casing, thereby preventing the drilling mud pumped in at high pressure from escaping upward through the grip head.

In order to ensure this, provision can be made in a preferred embodiment whereby in response to inflating the bladder an annular space is sealed off to the drilling mud that is formed between the circulation pipe and an introduced casing coaxially surrounding the circulation pipe. What is preferably achieved by the inflating action is that the bladder increases in volume, continues to inflate, and thus contacts the inner surface of the casing wall and the outer surface of the circulation pipe wall, thereby sealing this annular space in a pressure-tight fashion. Here the seal against circulating pressures of varying levels can be achieved, in particular by the pressure used to inflate the bladder. In terms of the fluid to be pumped into the bladder, water, for example can be used; however, preferably, a hydraulic fluid, in particular an oil is used.

In order to enable this inflation, provision is made in a preferred embodiment whereby the annular bladder is composed of a flexible, in particular elastic material. The flexibility ensures that when inflated the bladder automatically adjusts to the shapes that exist in the annular space between circulation pipe and casing.

In addition, the preferred elasticity of the bladder ensures that fluid pumped into the bladder also automatically then escapes from the bladder due to the fact that the inflated elastic material tends to contract and thus force the pumped-in fluid out of the bladder.

Provision can, however, also be made whereby the fluid for inflation is not only pumped into the bladder but the fluid is also pumped out of the bladder to relieve the pressure. Both for pumping to inflate, and optionally pumping the fluid out, a separate pump can be used, but also a pump that is employed in any case for an earth-drilling system having this type of grip head according to the invention.

Provision can be made in another preferred embodiment whereby the bladder is attached to the circulation pipe, thereby preventing the bladder from moving axially relative to the circulation pipe, in particular when not inflated. The attachment thus always achieves the optimum position relative to the circulation pipe and relative to an inserted casing. In particular the attachment can be selected so that the bladder is above the lower end of the circulation pipe and simultaneously relative to a casing inserted into the grip head below the upper end of the casing.

In an embodiment according to the invention, the bladder has a fluid supply line that is able to be supplied with fluid from a rotary feedthrough fitting attached to the circulation pipe. For example, this rotary feedthrough fitting can have an inner fluid-conducting annular part that is rotationally fixed to the circulation pipe and is connected do the fluid supply line, and has an outer fluid-conducting annular part rotatable relative to the inner annular part, which is rotationally fixed to a surrounding machine assembly and through which fluid is supplied to the inner annular part when the annular parts rotate relative to each other.

This ensures that no twisting of the fluid supply line occurs around the circulation pipe or relative to the grip head when the grip head rotates so as to drill a casing into the ground since the fluid supply line extends between the bladder and a part of the rotary feedthrough fitting that is rotationally fixed to the circulation pipe with the result that the fluid supply line rotates together with rotation of the grip head.

The delivery of fluid to the rotary feedthrough fitting and then to the bladder can be effected by a surrounding machine assembly through an outer rotatable annular part on the feedthrough fitting, this part being rotationally fixed relative to the surrounding machine assembly, where here too the rotational decoupling between outer and inner annular parts ensures that the delivery to the rotary feedthrough fitting and its outer annular part does not experience any twisting in response to rotation of a grip head relative to a surrounding machine assembly.

A preferred development of the rotary feedthrough fitting can provide that this feedthrough fitting has three fluid conduits; in particular three rotary feedthrough fittings are thus technically implemented in one part. Accordingly, the ability is thus created by this rotary feedthrough fitting to deliver three different working fluids independently from the outside, i.e. from a surrounding machine assembly, to a rotating grip head. For example, provision can for example be made whereby one fluid conduit handles the fluid supply line and/or fluid discharge to and/or from the bladder, where two other fluid conduits are used to deliver fluid to at least one cylinder-piston unit each for axial movement of the sleeve on the tube in opposite directions.

For example, actuation of the grab means of the grip head can be effected by movement of the movable sleeve relative to the tube, where at least one cylinder-piston unit is provided to actuate the sleeve for movement axially for each of the two possible directions. Thus, at least one cylinder-piston unit can be used to move the sleeve downward relative to the tube, and at least one other can be used to move the sleeve upward relative to the tube. Each of these cylinder-piston units can receive its working fluid from one of the conduits of the above-referenced rotary feedthrough fitting. The ability thus exists to deliver all requisite working fluids to the grip head according to the invention using only a single rotary feedthrough fitting.

An embodiment of the invention is illustrated in detail in the following FIGURE.

FIG. 1 here provides a schematic sectional view of a grip head according to the invention that comprises a tube 3 on which is coaxially mounted a sleeve 1, a so-called a grip head cap whose lower end widens downward in a frustoconical funnel shape. The inner wall region of this downwardly flared lower end of the movable sleeve forms actuating surfaces for radially outer ends or abutment faces of jaws 2 that are thus automatically moved radially inward by axial downward movement of the sleeve. These clamping jaws 2 can be movably mounted on the sleeve 1 and/or on the tube 3.

FIG. 1 shows a casing 9 inserted in the grip head according to the invention, where the jaws 2 bear radially inward on the outer surface of the casing 9 due to the downward displacement of the outer sleeve 1 and create a frictional and/or nonpositive engagement. This creates the ability to transmit torque to the casing 9 by rotating the entire grip head according to the invention to insert the casing by rotation into a borehole.

FIG. 1 furthermore shows second grab means that is formed by multiple inner wedges 4 arranged around the casing 9, where each inner wedge 4 has a radially outwardly directed guide face 4 a that bears on a radially inwardly directed guide face 3 a formed in the tube 3, thereby enabling radial movement of the inner wedges, in particular inward, to be effected by moving the respective inner wedge 4 axially, in particular downward.

As mentioned above, the individual inner wedges 4 of the second grab means are moved when the sleeve 1 outside the tube 3 moves axially downward, in particular in the normal working position. To this end, a mechanical linkage is provided that extends, for example, through the wall of the tube 3 between the outer sleeve 1 and inner wedges 4.

This ensures that, when the outer sleeve 1 is moved on the tube 3, the inner wedges 4 on the tube 3 are entrained to move in the same direction at least to a limited extent.

The relative orientation of the guide faces 3 a and 4 a of the tube 3 and of the inner wedges 4 here has the effect that axial movement automatically causes radial movement of the inner wedges 4 such that they bear in positive engagement against the casing 9 enclosed by the tube.

The kinematic translation of an axial movement effected by the inner wedges 4 into a radial inward movement can be effected here, for example, in that the engaged guide faces 3 a and 4 a on the inner wedges 4 and the tube 3 are inclined relative to the central axis of the tube 3, in particular are at an acute angle thereto when viewed in cross-section.

A positive engagement between the inner wedges 4 and the casing 9 can be achieved here by contact faces 4 b that are provided on the inner wedges 4 and their radial inner end faces that are shaped complementarily to the casing 9, in particular at their upper ends, for example, to the diameter of the casing 9, with the result that these contact faces 4 b, have for example at least one cylindrical-section-type surface region, and/or can also be formed with a shoulder 9 a that fits with the casing, or have a step 9 a at which the diameter of the casing changes, in particular is reduced from top to bottom.

This reduction at the referenced shoulder or step 9 a can be effected, for example, by a right-angle step relative to the axis of the casing, or also by a conical step or possible other shapes. Accordingly, the contact faces 4 b of inner wedges 4 have portions that are adapted to this type of shoulder or step 9 a, thereby enabling an axial lifting force or retaining force to be exerted on the casing by positive engagement between the inner wedges 4 and the casing 9, due to the fit of the inner wedges 4 with this shoulder or step 9 a when the contact face 4 b engages the shoulder or step 9 a without the inner wedges 4 sliding axially relative to the casing 9.

In order to form the guide face 3 a as an opposing surface for those guide faces 4 a on each inner wedge 4, provision can be made in the embodiment shown here whereby this guide face is formed inside the tube 3 by a radially inwardly projecting annular ridge 3 b whose inner periphery forms a frustoconical inner face that is coaxial to a central axis M of the tube 3, in particular such that this frustoconical inner face tapers downward in the normal working position of the grip head. It is specifically this downward taper that achieves the result that movement of these inner wedges 4 radially inward is effected in response to their downward movement in the grip head when the guide faces 4 a of the inner wedge 4 slide along the frustoconical inner face 3 a of the annular ridge 3 b.

The design of a frustoconical inner face on the inner annular ridge inside the tube has advantages in terms production engineering since this type of frustoconical inner face can be easily effectuated by internally turning out a shaft. To this end, for example, a the tube 3 can be produced from a solid material.

The radially outwardly directed guide faces 4 a of inner wedges 4 can furthermore be designed as outer conical outer surface regions corresponding to the frustoconical inner face. This is the result when both guide faces 4 a on inner wedges 4 as well as those on the projecting annular ridge are of frustoconical shape, or form a section of a frustoconical inner face, such that there is only one specific position at which respective guide faces 4 a of inner wedge 4 and annular ridge 3 b contact each other in positive engagement since outside this specific position the respective diameters of the individual conical surfaces do not match each other relative to central axis M of the tube 3.

Provision is therefore made in a preferred embodiment whereby the guide faces 3 a and 4 a of inner wedge 4 and annular ridge 3 b are complementary to each other in such a way that the positive surface-contact engagement between these guide faces increases with increasing positive engagement between inner wedges 4 and the casing 9, that is, in particular when the inner wedges 4 are pushed downward and simultaneously inward by the sleeve 3.

The second grab means can thus be implemented such that at the moment when an optimal positive engagement exists between the inner wedges 4 and the casing 9 an optimal positive engagement is also present between the guide faces 3 a and 4 a. In this way, forces are optimally transmitted between the surfaces while avoiding high local loads. This embodiment furthermore has the advantage that when no positive engagement yet exists between the inner wedge 4 and the casing 9, or between the respective guide faces, these guide faces do not contact each other over their entire surface areas but only at certain points or linearly, thereby reducing friction between the guide faces in this position of the inner wedges.

The same design can also be provided between the guide faces on the jaws 2 of the first grab means and the conically widening lower end of the outer sleeve 1. All of the above-mentioned embodiments in terms of construction of the guide faces between the inner wedges of the second grab means and the frustoconical inner face of the annular ridge also apply analogously to the jaws 2 of the first grab means and the frustoconical downwardly flaring end of the sleeve 1.

In this embodiment, provision can furthermore be made whereby one inner wedge 4 is movable axially on a bolt 6 extending parallel to but offset from the tube axis M and passing through the one inner wedge 4 or a projection extending radially therefrom. This has the advantage when multiple individual inner wedges 4 are used these elements are guided and can move only axially along this guide inside the tube 3.

As a result, for example, any tilting of the inner wedges 4 relative to the casing 9 is prevented. In order to enable an approach where, in addition to the guided axial movement, at the same time radial movement, in particular inwardly, is possible, the bolt 6 is located in a slot of the inner wedge 4 or its above-referenced projection that is elongated radially, in other words, for example, analogously to a radially elongated slot. As a result, given axial movement of the inner wedge 4 it can be guided axially along the bolt 6 and can simultaneously move radially perpendicular to the axial extent of the bolt 6.

As mentioned above, provision is made according to the invention whereby inner wedges 4 are actuated by movement of the outer sleeve 1. To this end, a linkage can be provided from inside the tube 3 to outside the sleeve 1. In the embodiment shown, the inner wedges 4 here are movable axially, in particular in the direction of increasing positive bearing on the casing by an actuating element 5 provided inside the tube 3, the actuating element 5 being connected to the sleeve 1 outside the tube by at least one radial link that extends through an slot 3 c in the tube 3.

Provision is preferably made here whereby this slot 3 c is elongated axially of the tube 3 so that in response to axial movement of the sleeve 1 a link that extends radially through this slot 3 c can shift axially in the slot 3 c. As a result, movement of the sleeve 1 outside the tube 3 can be transmitted into the tube 3 due to the fact that the actuating element 5 connected by the links moves together with the sleeve 1. The movement of the actuating element 5 can thus be transmitted in various ways to inner wedges 4, for example by having the actuating element 5 act directly and immediately on the inner wedges 4 or by having the actuating element 5 act indirectly through intermediate elements on the inner wedges 4.

Independently of the manner of this action, provision can be made here in a preferred embodiment whereby the actuating element 5 is a ring with a central hole surrounding the casing, and with all the inner wedges 4 movable this actuating element 5.

Provision can furthermore be made whereby the above-referenced bolts 6, along which the inner wedges 4 move, are attached to the actuating element 5. For example, attachment can be effected by a screw connection, or the bolts 6 can extend in guide holes provided on the annular ridge 3 b formed in the tube and forming the frustoconical outer guide face. The bolts 6 here angularly equispaced around and radially equispaced from the central axis M, as are the respective inner wedges 4 that are movably mounted thereon.

In another preferred embodiment, at least one of the inner wedges 4, in particular each inner wedge in the tube 3, can be biased against a resetting force in the direction of increasing positive engagement and thus, in particular in a downward direction in terms of the normal working position. This resetting force can be exerted, for example, by a compression spring 7, in particular one that is supported at one end, in particular at its lower end, on the respective inner wedge 4, and is supported at its opposite end, in particular at its upper end, on the annular ridge mentioned above. This compression spring 7 can surround the respective bolt 6, also referenced above.

The movement by the inner wedges 4 in the direction of increasing positive engagement against a resetting force has the advantage that the inner wedges 4 can be pressed axially against a shoulder or step 9 a formed on the casing by this resetting force. This produces the effect whereby, at the moment when the casing releases the inner wedges 4, the inner and outer guide faces are moved out of engagement by the resetting force, in other words, are shifted upward for example, relative to the normal working position. As a result, the casing is released from the inner wedges 4. This type of release between the casing 9 and the inner wedge 4 can be effected, for example when the casing 9 is inserted into the ground and the grip head moves downward relative to the casing 9 away from shoulder 9 a of the casing 9 a axially of the casing 9.

In the embodiment shown here, which can also be dispensed with, provision is made whereby an indirect action by actuating element 5 on respective inner wedges 4 is implemented by at least one compression spring 8 that is provided between the actuating element 5 and the inner wedges 4. This achieves the effect that a force does not act directly between the actuating element and the inner wedges but the force instead is applied in each case by a respective one of the compression springs 8. This has the additional advantage that essentially the same force is always exerted on each inner wedge 4 through a given specified axial travel, the force being produced by the spring constant of the respective compression spring 8 as a function of the compression travel.

In an embodiment not shown here, provision is made whereby this type of compression spring 8 is disposed directly between actuating element 5 and inner wedge 4, or, on the other hand, in an especially preferred embodiment shown here, whereby this type of compression spring 8 is disposed between an actuating element 5 and an intermediate element 5 a, for example an intermediate ring 5 a located between the actuating element 5 and the inner wedges 4. All the inner wedges 4 can in turn be contacted through this intermediate ring 5 a. The spring elements 8 can accordingly be provided between the annular end faces of the intermediate ring 5 a and the actuating element 5, for example, preferably where the above-referenced bolts 6 extend starting from actuating element 5 through intermediate ring 5 a and inner wedges 4. For example, each of these springs 8 can thus surround a respective one of the bolts 6.

This embodiment has the particular advantage according to the invention that the sleeve 1 is movable axially relative to the tube 3, where initially the inner wedges 4 are movable into a positive engagement with the casing 9 due to the indirect action of inner wedge 5 through compression springs 8, where an axial range of movement remains after this positive engagement is achieved between the actuating element 5 and the inner wedge 4, or between the actuating element 5 and the intermediate ring 5 a.

This axial travel essentially results here due to the fact that the compression springs 8 are not compressed completely when positive engagement is achieved. An axial travel thus remains that is provided by the compression of compression springs 8 achieved during positive engagement up to the maximum possible compression of compression springs 8, for example when their coils contact each other or a separate stop is provided. The construction of the grip head according to the invention is therefore such that due to this remaining travel the outer sleeve 1 is able to continue moving axially within this given travel even when there is positive engagement between the inner wedges 4 and the casing until an effective engagement is created between jaws 2 of the first clamping device and the casing 9. This effective engagement can be provided, for example, by a nonpositive, positive, and/or frictional engagement between the jaws 2 of the first clamping device and the casing 9.

What is thus effected during movement of the sleeve 1, in particular axially downward relative to the normal working position, is first a positive engagement to axially secure in place the casing 9 to the second grab means, and, once this is achieved, the effective engagement between jaws 2 of the first clamping device and the casing 9 in response to a further movement by the sleeve 1, thereby enabling torque to be transmitted.

When carrying and manipulating the casing 9, this type of grip head according to the invention thus provides not only the lifting forces exerted for this purpose but also at the same time the ability to rotate the casing due to the capability of transmitting torque, thus reducing adhesion between the casing 9 and the ground, and significantly facilitating the process of insertion.

When there is reverse movement by the sleeve 1, i.e. upward relative to the normal working position, the positive engagement between the jaws 2 and the casing 9 is thus first released in the reverse order, where in this case when the casing 9 is suspended the positive engagement is initially maintained between the inner wedges 4 of the second clamping device and the drill pipe, since the casing is supported by its weight on the inner wedges 4 through its shoulder/step 9 a described above, and these elements are thus loaded, instead of through the sleeve/actuating element, through the casing axially downward and thus in the direction of gravity, with the result that the positive engagement is maintained in a self-locking fashion.

It is only in the first case mentioned above, when the casing releases the inner wedges 4, that the grip head drops relative to the casing, with the result that the positive engagement between the casing 9 or shoulder 9 a and inner wedges 4 is removed, and inner wedges 4 are moved upward axially by the spring load, thereby releasing the casing.

Provision is preferably made in the device according to the invention whereby the second grab means is above the referenced first grab means relative to a normal working position of the grip head. It is also possible to reverse this arrangement.

In FIG. 1, the grip head according to the invention illustrated here furthermore has a circulation pipe 14 rotationally fixed to this grip head and extending coaxially of the central axis M through the grip head, and a cover plate 15 extending across the upper end of the tube 3 and rotationally fixed thereto.

The lower end of the circulation pipe 14 here terminates inside 1 the grip head according to the invention, or below the lower end of the tube 3, thereby always ensuring that the casing 9 introduced from below into the grip head according to the invention, which casing coaxially surrounds circulation pipe 14, engages with its upper end above the lower end of the circulation pipe 14. Provision is made here whereby the upper end of the casing 9, and in particular a step or shoulder 9 a disposed on this upper end, can be gripped securely by the above-described inner wedges 4, thereby securing in place the casing axially.

FIG. 1 here furthermore reveals that a bladder 11 of annular design is disposed in the annular space between the circulation pipe 14 and the casing 9, which bladder has a fluid supply line 12 that also extends through the top cover plate 15 and is attached here to an inner annular part of a rotary feedthrough fitting 13, this inner annular part being designed to be rotationally fixed to circulation pipe 14. Inflation of the bladder 11 can thus be achieved by the fluid supply line to the rotary feedthrough fitting 13, with the result that the annular space between the circulation pipe 14 and the casing 9 can be sealed against the drilling mud that is pumped into the casing 9 through the circulation pipe 14. The pumped-in drilling mud thus can only move downward inside the casing 9 and cannot move upward past the bladder 11, with the result that the drilling mud in the casing 9 is only pumped downward and lubricates the borehole, thereby ensuring easier insertion of the casing 9 into the borehole. In particular the inflated bladder ensures that any built-up pressure of the drilling mud is maintained completely within the casing 9.

As was mentioned above but not illustrated in the FIGURE, the rotary feedthrough fitting 13 can have not only one conduit to conduct fluid but optionally multiple conduits, in particular two additional conduits, in order to operate cylinder-piston units not shown here so as to move the outer sleeve 1 axially relative to the tube 3.

The constructive design of the grip head according to the invention as presented here can thus ensure that a casing is secured in place axially by the second grab means in the grip head described here and also that a transmission of torque to the casing can be effected by the first grab means with jaws 2, where at the same time drilling mud can be applied through the circulation pipe into the casing and a seal continues to be assured between circulation pipe and casing.

It must be stated in regard to all of the embodiments that the technical features referenced in connection with an embodiment can be employed or are employed not only in the specific embodiment but also in the other embodiments. All of the disclosed technical features of this description of the invention must be classified as essential to the invention and can be applied either in any combination with each other or alone. Throughout the entire disclosure, an implementation of the invention is also understood by the fact of mentioning that a feature can be provided, or that a method step can be implemented in which the relevant feature is provided, or a relevant method step is performed. 

1. A grip head for an earth-drilling system, the grip head comprising a tube, a sleeve provided coaxially on the tube so as to move relative thereto and having a downwardly frustoconically widening lower end, at least two jaws supported in the tube on the sleeve so as to move radially but not angularly relative to the tube, the jaws having radially outer ends having abutment faces that interact with the widening lower end such that by sliding the lower end over the jaws they are pressed radially inward and form first grab means for an upper end of a casing that is insertable/inserted into the sleeve for transmitting torque between the jaws and the casing and thus between the tube and the casing, second grab means provided in the tube for securing the casing axially at its upper end so as to hold the casing stationary axially against gravity relative to the grip head, a circulation pipe for the delivery of a drilling mud extending coaxially in the tube and rotationally fixed thereto, an annular bladder inflatable by a fluid surrounding the lower end of the pipe, and means connected to the bladder for inflating it with a fluid and thereby sealing an annular space between the casing and the tube for preventing upward escape of drilling mud from inside the casing through the grip head.
 2. The grip head according to claim 1, wherein the second grab means is actuatable by moving the sleeve.
 3. The grip head according to claim 1, wherein the sleeve for actuating the first grab means is movable relative to the tube by a first drive and the second grab means is actuatable by a second drive independent of the first drive, both drives being attached to a common support element.
 4. (canceled)
 5. The grip head according to claim 1 wherein the annular bladder is composed of a flexible elastic material.
 6. The grip head according to claim 1 wherein the bladder is attached to the circulation pipe.
 7. The grip head according to claim 1, wherein the bladder has a fluid supply line supplied with the fluid from a rotary feedthrough fitting attached to the circulation pipe, in particular an inner annular part that is rotationally fixed to the circulation pipe, and is connected to the fluid supply line, and has an inner annular part that is rotationally fixed relative to a surrounding machine assembly, and by which fluid is able to be supplied to the inner annular part.
 8. The grip head according to claim 7, claim 7, wherein the rotary feedthrough fitting has three fluid conduits, wherein one fluid conduit is provided for the fluid supply line to the bladder, and two fluid conduits are provided for delivery of fluid to at least one each of two cylinder-piston units for axial movement of the sleeve on the tube in opposite directions.
 9. The grip head according to claim 1, wherein the second grab means comprises at least two inner wedges each of which has a radially outwardly directed guide face that interacts with a guide face provided inside the tube with the result that radial inward movement is effected by moving a inner wedge axially downward.
 10. The grip head according to claim 1, wherein the inner wedges each have a radially inwardly directed frustoconical contact face formed as a shoulder or step, by which they can each be applied radially with positive engagement to an upper end of a casing.
 11. The grip head according to claim 10, wherein the shoulder or step is of right-angled shape formed by a collar that surrounds the upper end of the casing a lower end face of the collar forming the shoulder or step. 